Résumé
High-voltage cathodes such as LiMn1.5Ni0.5O4 (LNMO) offer promising energy density but suffer from interfacial degradation accelerated at elevated voltages and temperatures. Here, we present a comprehensive comparative study of three Li3PO4 coating methods (precipitation, sol–gel, and dry sol–gel routes) applied to commercial LNMO powders. Coating quality and intimacy are systematically assessed using a correlative, multitechnique approach including 7Li and 31P solid-state NMR, X-ray diffraction, and electrochemical testing. A key insight from this study is the use of ssNMR relaxation behavior as a sensitive probe of coating intimacy to the active phase. The methodology is validated on commercial LNMO and reproduced in a lab-synthesized LNMO to demonstrate reproducibility across particle morphologies. Among all methods, the sol–gel route produced a uniform ∼20 nm coating with optimal surface contact, translating to improved rate capability and outstanding high-temperature cycling stability (87% retention after 100 cycles at 50 °C compared to 29% for the non-coated LNMO), while retaining rate capability. These findings establish a practical framework for designing robust interfacial coatings in high-voltage lithium-ion battery materials.